1. Field of the Invention
The present invention relates to a magnetic detecting element such as a spin valve thin film element mounted on a hard disk device or the like. Particularly, the present invention relates to a magnetic detecting element comprising a pinned magnetic layer and first antiferromagnetic layer whose structures are optimized for properly pinning magnetization of the pinned magnetic layer, improving reproduction output, and properly complying with a narrower gap, and a method for manufacturing the magnetic detecting element.
2. Description of the Related Art
FIG. 63 is a partial sectional view of a conventional magnetic detecting element (spin valve thin film element), as viewed from a surface facing a recording medium.
In FIG. 63, reference numeral 1 denotes an antiferromagnetic layer made of PtMn or the like, a pinned magnetic layer 2 made of a NiFe alloy, a nonmagnetic material layer 3 made of Cu, and a free magnetic layer 4 made of a NiFe alloy being laminated on the antiferromagnetic layer 1.
As shown in FIG. 63, permanent-magnet layers 5 are formed on both sides of these layers in the track width direction (the X direction shown in the drawing), the layers ranging from the antiferromagnetic layer 1 to the free magnetic layer 4, and electrode layers 6 are formed on the respective permanent-magnet layers 5.
In the magnetic detecting element shown in FIG. 63, magnetization of the pinned magnetic layer 2 is pinned in the Y direction shown in the drawing by an exchange coupling magnetic field produced between the antiferromagnetic layer 1 and the pinned magnetic layer 2. On the other hand, magnetization of the free magnetic layer 4 is oriented in the X direction by a longitudinal bias magnetic field from each of the permanent magnet layers 5 provided on both sides of the free magnetic layer 4.
When an external magnetic field enters into the magnetic detecting element shown in FIG. 63 from the Y direction, the magnetization of the free magnetic layer 4 varies to exhibit a magnetoresistive effect in relation to the pinned magnetization of the pinned magnetic layer 2 magnetized in the height direction (the Y direction), reproducing an external signal.
However, the structure of the magnetic detecting element shown in FIG. 63 has the following problems.
A sensing current from the electrode layers 6 preferably mainly flows through the nonmagnetic material layer 3 without shunting to the antiferromagnetic layer 1. However, in the structure shown in FIG. 63, the sensing current easily shunts to the antiferromagnetic layer 1 formed below the bottom of the pinned magnetic layer 2 to cause a current loss, thereby causing the problem of decreasing reproduction output. In the magnetic detecting element shown in FIG. 63, a track width Tw is determined by the width dimension of the upper surface of the free magnetic layer 4 in the track width direction (the X direction). However, the decrease in reproduction output becomes more significant as the track width Tw decreases, and thus a shunt sensing current shunting to the antiferromagnetic layer 1 has a considerable problem.
Also, the antiferromagnetic layer 1 is thicker than the layers laminated thereon. One of the reasons for this is that a large exchange coupling magnetic field is produced between the antiferromagnetic layer 1 and the pinned magnetic layer 2, for appropriately pinning the magnetization of the pinned magnetic layer 2. However, the above-described current loss increases due to the large thickness of the antiferromagnetic layer 1, and the distance between shield layers 7 and 8 formed at the top and bottom of the magnetic detecting element in the thickness direction (the Z direction shown in the drawing) cannot be decreased, failing to manufacture the magnetic detecting element adaptable for a narrower gap.
Furthermore, as shown in FIG. 63, when the antiferromagnetic layer 1 is formed below the entire bottom of the pinned magnetic layer 2, a magnetic detecting element resistant to electrostatic damage (ESD) cannot be manufactured. This is because a sensing current from the electrode layers 6 generates heat in the element, and magnetization of the pinned magnetic layer 2 which should be pinned in the Y direction is easily fluctuated by the effect of a transient current due to the ESD. Heat generation to a temperature lower than the blocking temperature of the antiferromagnetic layer 1 is not a large problem. However, at present, the element decreases in size, and thus heat at a temperature over the blocking temperature is generated in the element, thereby causing a magnetic electrostatic damage phenomenon called “soft ESD” in which the exchange coupling magnetic field produced between the antiferromagnetic layer 1 and the pinned magnetic layer 2 weakens to fluctuate the magnetization of the pinned magnetic layer 2.
The structure of an exchange coupling film comprising the pinned magnetic layer 2 and the antiferromagnetic layer 1 is not limited to a simple structure in which the two layers are simply laminated as shown in FIG. 63. An improved structure of the above-described structure of the exchange coupling film, and a self pinning-system pinned magnetic layer are disclosed in some documents.
For example, FIG. 64 illustrates a magnetic detecting element transcribed from FIG. 1 of Japanese Unexamined Patent Application Publication No. 2000-163717 (referred to as “Patent Document 1” hereinafter). FIG. 64 is a partial sectional view of the magnetic detecting element, as viewed from a surface facing a recording medium. In FIG. 64, the same reference numerals as in FIG. 63 denote the same layers as in FIG. 63, and reference numerals 9 and 10 each denote a gap layer.
As shown in FIG. 64, the antiferromagnetic layer 1 has a thin portion 11 provided at its center in the track width direction and different in thickness from both sides. Patent Document 1 discloses that the thin portion 11 has a weak force for directly pinning the magnetization of the pinned magnetic layer 2, while the magnetization pinning force exerted in both side portions of the antiferromagnetic layer 1 having a sufficient thickness compensates for the weak magnetization pinning force in the central potion of the pinned magnetic layer 2, thereby preventing deterioration in characteristics.
However, the above-described problems remain unsolved by the structure of the magnetic detecting element disclosed in Patent Document 1. Even if the thin portion 11 is formed at the center of the antiferromagnetic layer 1, the sensing current from the electrode layers 6 shunts to the thin portion 11 to cause a current loss, and electrostatic damage also easily occurs. Also, when the thin portion 11 is formed at the center of the antiferromagnetic layer 1, the exchange coupling magnetic field produced between the antiferromagnetic layer 1 and the pinned magnetic layer 2 decreases to apparently decrease the force of pinning the magnetization of the pinned magnetic layer 2, as compared with the force of pinning the magnetization of the pinned magnetic layer 2 of the magnetic detecting element shown in FIG. 63.
If the thin portion 11 of the antiferromagnetic layer 1 is significantly decreased for decreasing the current loss, the exchange coupling magnetic field does not occur between the thin portion 11 and the pinned magnetic layer 2. Therefore, even when magnetization is strongly pinned between both side portions of the pinned magnetic layer 2 and the antiferromagnetic layer 1, as described in Patent Document 1, the magnetization of the central portion of the pinned magnetic layer 2 is controlled only by a bias magnetic field through an exchange interaction within the magnetic layer, and thus the magnetization of the central portion cannot be strongly pinned. Therefore, the magnetization of the central portion easily varies with an external magnetic field to possibly inevitably cause deterioration in the reproduction output.
FIG. 65 shows a portion of the magnetic detecting element transcribed from FIG. 5 of Japanese Unexamined Patent Application Publication No. 8-7325 (referred to as “Patent Document 2” hereinafter). FIG. 65 is a partial sectional view of the magnetic detecting element, as viewed from a surface facing a recording medium. In FIG. 65, the same reference numerals as in FIG. 63 denote the same layers as in FIG. 63.
The magnetic detecting element shown in FIG. 65 comprises the pinned magnetic layer 2 having a three-layer structure including two magnetic layers 12 and 14, and a nonmagnetic layer 13 interposed therebetween. In Patent Document 2, the pinned magnetic layer 2 is referred to as an “automatically pinned layer”. As shown in FIG. 65, the antiferromagnetic layer 1 for pinning the magnetization of the pinned magnetic layer 2 is not provided. Patent Document 2 discloses that the two magnetic layers 12 and 14 constituting the pinned magnetic layer 2 are magnetized in opposite directions and automatically pinned, and the magnetizations of the magnetic layers 12 and 14 are not rotated even when an external applied magnetic field enters.
However, when the magnetization of the pinned magnetic layer 2 is pinned only by a magnetic field produced between the magnetic layers 12 and 14 of the pinned magnetic layer 2 without using a bias means such as the antiferromagnetic layer 1, as shown in FIG. 65, the magnetizations of the magnetic layers are easily rotated by various factors such as the magnitude of the external magnetic field, etc. while maintaining an antiparallel state, or the antiparallel state is easily broken to cause deterioration in the reproduction output.
Even when the pinned magnetic layer 2 has the above-described three-layer structure, the degree of a magnetic moment per unit area of each of the magnetic layers 12 and 14 necessary for causing the pinned magnetic layer 2 to function as the “automatically pinned layer” described in Patent Document 2 is not apparently defined.
The magnetic detecting element disclosed in Japanese Unexamined Patent Application Publication No. 8-7235 (referred to as “Patent Document 3” hereinafter) comprises a buffer layer serving as an underlying layer and made of tantalum (Ta), and a pinned ferromagnetic layer laminated thereon. The pinned ferromagnetic layer comprises a first cobalt (Co) film and a second cobalt (Co) film which are laminated with a ruthenium (Ru) film provided therebetween. The magnetization of each of the first and second cobalt (Co) films is pinned by an anisotropic magnetic field. The first and second cobalt (Co) films are antiferromagnetically coupled with each other and magnetized in antiparallel directions.
However, it was found that in the structure of the magnetic detecting element disclosed in Patent Document 3 in which the Co films are laminated on the buffer layer made of tantalum, the magnetization direction of the pinned ferromagnetic layer cannot be appropriately pinned. This is also suggested in Japanese Unexamined Patent Application Publication No. 2000-113418 (referred to as “Patent Document 4” hereinafter).
The magnetic detecting element disclosed in Patent Document 4 is devised for solving the problem of Patent Document 3. In the magnetic detecting element, a ferromagnetic film of a laminated ferrimagnetic pinned layer is made of CoFe or CoFeNi to improve induced anisotropy.
Patent Document 4 also discloses that an underlying layer made of Ta is provided below the laminated ferrimagnetic pinned layer. However, the results (FIGS. 4, 5, 6, and 7 of Patent Document 4) of the experiments carried out for comparing a case using the Ta underlying layer and a case not using the Ta underlying layer indicate that in the use of a CoFe alloy for the ferromagnetic layer, both a change in magnetoresistance and coercive force are increased when the Ta underlying layer is not provided.
Patent Document 4 also discloses that in order to increase the induced anisotropy of the laminated ferrimagnetic pinned layer, a CoFe alloy is used for the ferromagnetic film, and magnetostriction of the ferromagnetic film is made positive.
The most important factor for pinning the magnetization of the self pinning-system pinned magnetic layer is uniaxial anisotropy derived from the magnetoelastic energy of the pinned magnetic layer. Particularly, it is important to optimize the magnetostriction of the pinned magnetic layer. However, in Patent Document 4, no consideration is given to a mechanism for optimizing the magnetostriction of the pinned magnetic layer, and a specific structure for optimizing the magnetostriction of the pinned magnetic layer is not described.
As described above, there has been conventionally no structure capable of strongly pinning the magnetization of a pinned magnetic layer, improving reproduction output, and appropriately complying with a narrower gap and electrostatic damage.